May 30 the oats fields were revisited by Mr. Kelly, in company 
with Mr. C. A. Hart, whom I had sent out from the office to inspect 
the situation , and to the astonishment of both not an ant nor an 
aphis could be found in the whole forty-five acres of this crop. As 
recent rains had fallen, it was at first surmised that the ants' bur- 
rows had merely been obliterated, but protracted search on the two 
following days, which were warm and bright, gave the same nega- 
tive result. The smartweeds were now virtually all dead, and the 
oats were tall enough to shade the ground. The entire ant and aphid 
population of these fields had evidently abandoned them, and could 
not be traced. 
June 22 another visit was made to this field, and prolonged 
search again failed to discover a single insect of either kind, al- 
though in the adjoining corn both ants and aphids were numerous, 
and in one of the fields, where nearly every hill was infested, con- 
siderable injury was being done. The field of corn which had been 
in oats the preceding year, and in which on previous visits ants were 
found but not a root-louse, was now badly infested, and this fact 
offered the only possible hint of the whereabouts of the insects which 
had left the oats the preceding month. 
Observations in the Thompson Field. — For further evidence 
concerning the effects of a change from corn to oats, observations 
were made by Mr. Kelly on two adjacent fields of forty acres each, 
one in corn this spring and the other in oats, both fields having been 
in corn continuously for the three years preceding, and both being 
heavily infested by Aphis maidiradicis May 8, when first selected 
for this comparison. 
May 19, the ground being very wet after a recent rain, eight ant 
hills were examined in the oats field and their contents collected. 
Three hundred and thirty-four ants were obtained, an average of 
forty-two to each colony, and one hundred and sixty-seven aphids, 
an average of twenty-one to each ant's nest. Fifty of these aphids 
were wingless adults and eight were pupa^, the remainder, of course, 
being young in various stages. These were contained in seven of 
the nests, one nest being without root-lice. The number varied from 
two to forty-six to a nest. 
The other field had been plowed for corn April 28 to May 5, 
and harrowed twice. Hard rains following, it was disked twice 
May 19 and 20, and harrowed again just as it was planted. Both 
ants and root-lice were found in this corn May 20, but no record was 
made of their number or distribution until June 2, at which time a 
final visit was made for a comparison of the tv/o fields. 
In the oats not an ant nor an aphid could now be found; even 
the borders of the field nearest the corn had been completely aban- 
